1. Field of the Invention
The present invention generally relates to a nanoimprinting method and a mold for use in nanoimprinting, and more particularly, to a nanoimprinting method and a mold which transfer a micropattern on a mold to a resin in a large area.
2. Description of the Related Art
Recently, a microprocessing technology for easily carrying out reverse transfer of a microstructure on a mold to a workpiece such as a resin or a semiconductor substrate has been developed and has received attention (see Stephen Y. Chou et. al., Appl. Phys., Lett., Vol. 67, Issue 21, pp. 3114-3116 (1995)).
This technology is called nanoimprint or nano-embossing, and a processing size thereof matches with the size of the microstructure of a mold. Transfer of structures from the order of micrometers to the order of 10 nm or less has been reported.
Principles of nanoimprinting are relatively simple, and the process may be carried out, for example, as follows.
First, a workpiece having a resin applied to a substrate (e.g., semiconductor wafer) is prepared. As such a resin, there may be utilized a photocurable resin, a thermoplastic resin, a thermosetting resin, or the like. After a mold having a predetermined unevenness pattern formed thereon is brought into contact with the workpiece, a resin is filled therebetween and is cured by ultraviolet light irradiation or through a heating/cooling step. Then, the mold is released to achieve reverse transfer of the pattern on the resin.
This technology can provide full transfer of a three-dimensional structure, and hence it is expected not only to be the next-generation semiconductor fabrication technology to replace light exposure apparatuses such as a stepper and scanner, but is also a promising technology for application to a variety of fields, such as application in an optical device, a bio device, a patterned medium, a display and the like.
In consideration of applying nanoimprinting to the above-mentioned applications, there may be a case where patterning of a large area is to be performed.
In such a case, while full transfer with a large mold is one way of patterning, a more suitable way may be a known step-and-repeat method of achieving sequential transfer using a mold smaller than a workpiece (see U.S. Pat. No. 7,077,992).
According to the method, designing a smaller mold can reduce the fabrication cost which is involved in enlargement in the size of molds.
Furthermore, a known resin application method which is adapted to the step-and-repeat method is a drop-on-demand method of applying a resin per each shot of nanoimprinting, as opposed to full application to the entire surface by spin coating (see U.S. Patent Application Publication No. 2005/0270312).
According to this method, the amount of a resin may be locally adjusted depending on the pattern density and shape of a mold, resulting in improved uniformity of thickness of the remaining film and improvement in the transfer accuracy.
However, execution of nanoimprinting with the step-and-repeat method applied to patterning of a large area may bring about the following issue.
That is, at the time of carrying out such nanoimprinting as described above, a resin may run out (or run off or protrude) from the end surface of a mold while being filled between the mold and the substrate, and the run-out resin, if present between adjacent patterns, may impair the accuracy in connecting the patterns to each other.
FIG. 7 illustrates an example of transfer of a periodic dot pattern by nanoimprinting that illustrates resin that has run-out or overflowed from between the mold and the substrate.
In the example illustrated in FIG. 7, a resin 401 is applied on a substrate 102 and is processed with a protruding mold 301 by step-and-repeat type nanoimprinting to pattern a large area.
In FIG. 7, X is the period of the dot pattern, and Y is an interval between adjacent shots (ranges in each of which transfer can be performed using the mold).
In general, it can be difficult to control spreading of a resin at the end surface of a mold in nanoimprinting, and there are cases where the resin may run or overflow out of the end surface of the mold, thus yielding a run-out resin 402.
The presence of such run-out resin 402 can make it difficult to bring the patterns of adjacent shots close to each other to a desired distance.
Specifically, the distance Y between shots may become greater than the period X of the dot pattern, and hence a complete periodic structure may not be attained in a large area.
This issue is not peculiar to a dot pattern, but may also apply to other periodic patterns, a continuous pattern such as line and space, and a free pattern. For the reason described above, the step-and-repeat method may cause difficulty in connecting adjacent patterns to each other to obtain a larger periodic pattern.